As a general rule, a motor vehicle suspension system comprises a suspension assembly supporting an axle and a vehicle wheel. A suspension thrust bearing unit is disposed in an upper portion of the suspension assembly, opposite to the wheel and the ground, and between a suspension spring and an upper support block attached to the body of the vehicle.
The suspension thrust bearing unit includes at least one rolling bearing.
The suspension thrust bearing unit enables transmission of axial forces between the spring and the body of the vehicle and, in the meantime, allows relative angular movement between the spring, which is mobile in rotation, and the fixed support block attached to the body.
To this end, the spring is supported by a spring seat provided on the suspension thrust bearing unit. More precisely, the suspension thrust bearing comprises a lower cap with a lower support surface resting on ending coils of the spring. The spring support surface comprises a radial surface to support axial force. The spring support surface may also comprise a tubular axial surface to support radial deformations and to ensure the spring centering.
It is known from US 2010/0014792 A1 and EP 2 152 531 B1 to provide a damping device axially and radially disposed between the spring and the spring support surface of the suspension thrust bearing unit. As shown in these documents, the damping device is attached to the lower surface of the unit. Damping device is made from a resilient material, such as rubber, thermoplastic elastomer (TPE), in particular thermoplastic polyurethane (TPU), melt processible elastomer (MPE).
However, such a damping device may have some disadvantages. Indeed, unless having a damping device of important thickness, the ending coil of spring causes high concentration of stress to the lower cap. This results in a risk of premature fatigue and cracking of lower cap that can cause malfunction of suspension thrust bearing unit.
The damping device may also have a relative displacement with respect to the lower cap, that can increase the damping device wear.